The present invention relates to oilfield tubular threaded connections. More particularly, this invention relates to improvements in the thread on both the pin and box of the threaded connection for minimizing thread wear and galling.
Manufacturers of oilfield tubulars are continually seeking improvements which will satisfy the customers needs. One of the major areas of customer complaints is excessive thread wear and/or galling. When excessive wear and/or galling problems occur, it is not known, in many cases, whether that galling and thread wear occurred due to unusual conditions under which the threaded connection was made up and/or broken apart, whether the problem may relate to quality control of the threaded connection, or whether some change might be made in the thread design to minimize or eliminate the problem. In many cases, the existence of excessive wear or galling can be noted, but the reason for the problem cannot be determined. Even when a wear and/or galling condition attributable to thread design and/or a makeup condition is recognized, those skilled in the art know a design change to correct one problem may create more serious problems in other areas.
Customers of oilfield products have noted that, under some conditions, tool joint wear, particularly in the middle sections of the threads of the tool joints, resulted in sharp crests while the end sections were relatively undamaged. Customer complaints regarding thread wear and galling sometimes referred to xe2x80x9cwhiskersxe2x80x9d which are fine metal whiskers created during a makeup operation under severe thread wear or galling conditions.
Those skilled in the art appreciate that excessive thread wear and galling can cause the oilfield tubular, which may be tubing or casing, to be rejected for use in the well. In other cases the worn thread may be xe2x80x9crefinishedxe2x80x9d. Oilfield tool joints are conventionally manufactured so that, should the thread be damaged or worn excessively, an entirely new thread can be recut on the tool joint. Even this solution has its own problems, however, since costs are associated with recutting the thread, and since new threads can be recut on a tool joint a limited number of times before the tool joint body lacks the dimensions which would allow another thread to be cut on the tool joint. A conventional pressure flank crest radius and both flank crest radius or a tool joint is thus disclosed in U.S. Pat. No. 4,549,754.
The disadvantages of the prior art are overcome by present invention, and improved oilfield connection is hereafter disclosed which minimizes thread wear and/or galling problems associated with many prior art connections.
The present invention relates to an improved threaded tubular connection, and particularly to the thread on the pin and box of the tubular connection, which may be a tool joint. Those familiar with oilfield tubulars recognize that connected threads on both the pin and the box have both a nonpressure or stab flank and a pressure or load flank, and that these flanks normally serve different purposes.
The present invention recognizes that any misalignment between the pin and the box may cause the corner of the thread flank on the pin to engage the flat thread surface of the thread flank on the box. The weight to the pipe or other tubular hanging in an elevator may thus be transmitted through this corner contact. When the pin is subsequently rotated in the box to make up the connection, the sharp corner of the thread flank on the pin may wipe away the thread compound and thus gouge or scrape the adjacent thread on the box, causing high thread wear and damage.
According to the present invention, the thread on both the pin and box is modified to substantially increase the crest radius of the stab flank of the thread. According to a preferred embodiment, the crest radius on the pressure flank of the thread is not modified, however, so that a high pressure flank bearing area is maintained. According to preferred embodiments, the crest radius of the stab flank of the thread is approximately four times the crest radius of the pressure flank, and in most applications would be at least two times and less than six times the radius of the pressure flank. In an exemplary application, the radius on the pressure flank is maintained at a conventional 0.015 inches, while the radius on the stab flank is increased to 0.065 inches.
An object of the present invention is to provide an improved oilfield tubular threaded connection which minimizes galling and/or high thread wear. A related object of the invention is improved life and reliability of an oilfield tubular connection.
It is a feature of the present invention that the improved threaded connection may be provided on tool joints which are conventionally subjected to high stress applications.
It is another feature of this invention that thread wear and galling may be minimized while still maintaining the bearing area of the pressure flank at its conventional level.
It is a significant advantage of the present invention that a thread modified pin member may be used on a conventional box member, and that similarly the improved thread design of the present invention may be employed on a box and may be then used with a conventional pin. Another significant advantage of the invention is that thread wearing and galling are minimized with no significant change in the cost of manufacturing or repairing the thread on either the pin or the box.
These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.